236 The Data on which we have to depend 
In difficult scientific questions to whom are the public and 
the Legislature to look, if not to the Philosophical Society ? 
And shall it be said that they have looked to us in vain? 
I am also induced on other grounds to bring this subject 
before you. 
It will not be forgotten that Messrs. Acheson and Christy, 
in their report on the Yan Yean Reservoir scheme, assumed 
that 10°69 inches of the rainfall of the Plenty basin would 
be available for the reservoir, while Mr. Hodgkinson clearly 
showed, by a reference to Mr. Charnock and Mr. Howard, 
who are the best recent authorities on the subject, that with 
a rainfall varying from 24 to 36 inches, the availabie rainfall 
for the average surface of England varies from 4°88 inches 
to 5°33 inches, the mean of which is 5:20 inches, with a mean 
rain of 30°6 inches. Thus these gentlemen have assumed 
for the Plenty basin an available rainfall more than double 
that of England. 
I had imagined, therefore, that Mr. Hodgkinson had 
demonstrated the fallacy of “the excessively small rate of 
evaporation assumed by those gentlemen,” and that their 
enormous estimate of the available rain was “utterly at 
variance with the recorded observations of all other meteor- 
ologists.” It appears, however, that they are by no means 
convinced of their error, and that they congratulate them- 
selves in the belief that they have arrived at the very same 
result with Mr. Hodgkinson, only by a different method. 
When the premises are so very opposite, it would be 
singular indeed if the conclusions were the same. 
T cannot, therefore, understand how they have deceived 
themselves into the belief that they have arrived at the same 
results with Mr. Hodgkinson, unless after this singular 
method. 
They assume double the amount of available rainfall that 
he does, and, at the same, time, they rely on Dr. Davey’s 
estimate of the evaporation from the reservoir, which 
is nine feet, while he rejects Dr. Davey’s estimate of 
the evaporation, and assumes five feet and a half from 
his own observations on a pond. But they altogether 
forget that, while they generously leave 9,386 gallons per 
minute for the use of the district, he only allows 500 gallons 
per minute, or an equivalent to eight inches in the reservoir, 
which is less than one-eighteenth part of what they allow; 
and they also forget that a mere coincidence in their results 
proves nothing in their favour; on the contrary, when similar 
results are obtained from data which are altogether dissimilar 
